Described are 6-cyclylmethyl- and 6-alkylmethyl-substituted pyrazolo3,4-dpyrimidines of the formula :as defined herein, processes for their preparation and their use for producing medicaments for treating impairment of perception, concentration, learning andor memory. According to one embodiment, a network computer client boots from a boot image provided by an NC server. Furthermore, the system can look up the tree for a key, wherein the key is associated with a journal ticket that represents a virtual address of an entry in the journal. The coating material is based on an organic material. Embodiments of the present invention can also be utilized to create more elaborate fiber optical switches such as an N\xd7N switch and a N2\xd7N switch.